We have prepared an extract of erythrocyte hemolysates obtained from spontaneously hypertensive rats that has profound effects on blood pressure and vascular tissue of normotensive animals. This fraction produces a hypertensive elevation of blood pressure in normotensive rats that may be maintained for a period of days or weeks beyond the termination of the injection of the material. In addition, the substance involved stimulates the in vitro uptake of lanthanum resistant calcium by aortic segments. Finally, we have observed that the addition of the substance to the bathing media produces a transient contraction followed by increased sensitivity in isolated aortic strips from normotensive animals. The proposed series of studies are to define the hemodynamic effects of the substance. Subsequently, studies will be conducted to determine primary and secondary loci of action of the substance in the intact animal. In addition to the investigation of the effects in the intact animal, we will characterize the influence of the substance on contractility and calcium metabolism of vascular tissue. The information obtained in this project will further our knowledge concerning hypertension and the regulation of blood pressure. It will establish the exact nature of the cardiovascular alterations induced by the hypertensive substance and provide insight into the mechanism.